This invention relates to improvements in inductor type synchronous motor driving systems for finely controlling the position and the rotating angle, in which the vector rotation angle of the supply power is accurately projected to the mechanical rotating angle and thus highly precise resolving control is readily achieved. That is, in the inductor type synchronous motor of nondistortion electromagnetic structure, the vector synthesis theory is strictly established and, at the same time, high accuracy resolution and smooth rotation are realized simply and uniquely through trigonometric functional power feed.
Prior art motors of this type are referred to as the stepping motor, having a plurality of driving windings and a device for feeding the motor rotationally and in a given sequence, with currents whose phases differ from each other. Among these motors is the type having a DC field means (i.e., DC field winding or permanent magnet), in addition to the driving windings of respective phases. The inductor type synchronous motor to be improved by this invention has a first inductor with an arrangement of first magnetic tooth group, and a second inductor with an arrangement of second magnetic tooth group, the motor further having winding slots for the driving windings and a unit magnetic path (or a magnetic salient) on the back of the magnetic tooth group of the first inductor.
In order to increase the number of steps per rotation, prior art techniques have employed a method of increasing the number of steps, R, (the resolution number R of the vector rotation angle) per cycle (electrical angle 2.pi.) of the feeding current or a method of increasing the number of teeth, Q.sub.2, of the second magnetic tooth group. Of the former method, the following methods have been proposed: (1) Method of increasing the number of phases, m, of the driving winding: (2) Method of increasing the number of combinations of windings to which power is fed, that is, n-phase excitation&gt;(n+1)-phase excitation; (3) Method of increasing the number of steps, N.sub.step, where current is fed for the respective phases in stepped waveforms.
These prior art concepts, however, are impracticable for the following reasons:
The relationship between the torque .tau.; produced and the rotation angle deviation (load angle) .delta. in the state of arbitrary power feeding to an m-phase inductor type motor is given as follows according to the torque curve plotted for the i-phase load angle .delta..sub.i of torque .tau..sub.i produced on the i-phase during power feed to the i-phase and on the principle of superposition: ##EQU1## where
.delta..sub.i : load angle for i-phase, having phase difference
.phi..sub.i on i-phase against total reference load angle
i.sub.i : feeding current to i-phase
.tau..sub.i : torque produced on i-phase
The curve of the torque produced on each phase for a given current has no trigonometric functional characteristic as indicated by curves B and C in FIG. 1. To increase the torque gain (gradient near the origin), the torque curve has been made as curve B by the use of uniform magnetic teeth. These curves have hitherto been considered as trigonometric functional characteristic for convenience sake or approximately. Furthermore, the curves offer no linear characteristic with respect to changes in the current fed.
The torque .tau..sub.i (.delta..sub.i) produced at a given load angle .delta..sub.i with current i.sub.i changed follows a nonlinear curve as indicated by curve A in FIG. 2. This curve shows an example of a characteristic referred to as a reluctance motor, i.e., the so-called variable reluctance type (VR type) motor having no DC field. This motor has a square characteristic in the small current region, and a saturation characteristic in the large current region. The pattern (ratio) itself of the curve varies by the load angle .delta..sub.i. Therefore, when the current is reduced, the characteristic changes from curve B to curve D as in FIG. 1, and the load angle at the maximum torque point shifts by .DELTA..sub.p.
In other words, even if the values of currents being fed are changed proportional to each other with respect to the individual phases on the basis of the state that a given current I.sub.O is fed to each phase, the stationary balance point moves as indicated by the curve in FIG. 3, resulting in an error .phi..sub..epsilon. due to variations in the current value I. This has made it impossible to change the feed current when the motor is driven under high-resolution control (minute control or vernier control). Accordingly, it has also been impossible to reduce the time taken to increase or decrease motor speed by producing a large torque during acceleration or deceleration of the motor.
Furthermore, when current feed per phase is given in n numbers of stepped waveforms as in FIG. 4(a), the steps .DELTA.i.sub.1 to .DELTA.i.sub.n differ from each other and must be adjusted for each motor. FIG. 4(b) shows by example the period for which the current for one phase is increased; the solid line i.sub.n denotes a current value, and the dotted line .DELTA.i.sub.n denotes the incremental value of each step. In these patterns, there are no simple functional relationships. In motors with the same number of phases and similar in construction to each other, their step patterns differ from each other. The adjustment of the step patterns for the individual motor requires extremely intricate skill because one stationary balance point interferes with another stationary balance point. Furthermore, it is impossible to change the total feed current I because no proportional relationship is established between the total current I and each of the steps .DELTA.i.sub.1 to .DELTA.i.sub.n.
For the above reasons, it has been difficult to accurately increase the number of resolutions by current ratio. Also, it has been impossible to drive a motor of different capacity or construction by the same power feed device or the same power feed control pattern. This has hampered the development of standard systems for driving inductor type synchronous motors.
In prior art techniques, the kind of magnetic teeth which intersect the winding of one phase is purposely limited to one in order to increase the torque gain or the maximum torque itself. In high precision minute resolution control, the feed power is purposely made nontrigonometric in function. This leads to intricate construction of the power feed device and makes its adjustment difficult. Simplifying the construction results in large error in minute resolution control, and the significance of resolution control would be lost.
In the prior art device, there is no linear proportional characteristic between the feed current vector rotation angle and the driving force (torque) balance point.
In the device of phase separation type, there is no composite field gap used in common, corresponding to the current vector rotation angle.
The torque (driving force) balance point is not determined by one-dimensional dynamics according to vector synthesis from the electrical direction of each phase and the produced torque of each phase.
In the prior art devices, the vector rotation angle is made to correspond to the torque balance point .theta..sub..tau. (although the vector rotation angle does not essentially correspond to the torque balance point in terms of linearity mapping). Such correspondence is attained by nonlogical function means through adjustments. This has required intricate adjusting procedures. In addition, power source fluctuation (current variations) affects the adjusted result. Further, such adjustment is required each time the device is installed in a different place. Still further, setting must be changed for each motor used, and the freedom of the system is considerably limited.
It is an object of the invention to realize minute resolution control with simplicity and high accuracy for inductor type synchronous motor devices which perform high-resolution control.